U.S. patent application number 11/049109 was filed with the patent office on 2006-08-03 for method to detect and predict metal silicide defects in a microelectronic device during the manufacture of an integrated circuit.
This patent application is currently assigned to Texas Instruments Incorporated. Invention is credited to Deepak A. Ramappa.
Application Number | 20060172443 11/049109 |
Document ID | / |
Family ID | 36757091 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060172443 |
Kind Code |
A1 |
Ramappa; Deepak A. |
August 3, 2006 |
Method to detect and predict metal silicide defects in a
microelectronic device during the manufacture of an integrated
circuit
Abstract
The present invention provides a method detecting metal silicide
defects in a microelectronic device. The method comprises
positioning (110) a portion of a semiconductor substrate in a field
of view of an inspection tool. The method also comprises producing
(120) a voltage contrast image of the portion, wherein the image is
obtained using a collection field that is stronger than an incident
field. The method further comprises using (130) the voltage
contrast image to determine a metal silicide defect in a
microelectronic device. Other aspects of the present invention
include an inspection system (200) for detecting metal silicide
defects and a method of manufacturing an integrated circuit
(300).
Inventors: |
Ramappa; Deepak A.; (Dallas,
TX) |
Correspondence
Address: |
TEXAS INSTRUMENTS INCORPORATED
P O BOX 655474, M/S 3999
DALLAS
TX
75265
US
|
Assignee: |
Texas Instruments
Incorporated
Dallas
TX
|
Family ID: |
36757091 |
Appl. No.: |
11/049109 |
Filed: |
February 2, 2005 |
Current U.S.
Class: |
438/14 |
Current CPC
Class: |
G01R 31/307
20130101 |
Class at
Publication: |
438/014 |
International
Class: |
H01L 21/66 20060101
H01L021/66 |
Claims
1. A method of detecting metal silicide defects in a
microelectronic device, comprising: positioning a portion of a
semiconductor substrate in a field of view of an inspection tool;
producing a voltage contrast image of said portion, wherein said
voltage contrast image is obtained using a collection field that is
stronger than an incident field; and using said voltage contrast
image to determine a metal silicide defect in a microelectronic
device.
2. The method as recited in claim 1, wherein said collection field
is at least about 8 percent stronger than said incident field.
3. The method as recited in claim 1, wherein a detection potential
used to generate said collection field is greater than an
electron-beam landing energy voltage that generates said incident
field.
4. The method as recited in claim 3, wherein said detection
potential is at least about 20 electron-Volts greater than said
electron-beam landing energy voltage.
5. The method as recited in claim 1, wherein said inspection tool
is configured to display said voltage contrast image with signals
corresponding to said metal silicide defects that are pipes or
nubs.
6. The method as recited in claim 1, further comprises producing a
second voltage contrast image for said portion, wherein said second
voltage contrast image is obtained using a second collection field
that is weaker than a second incident field.
7. The method as recited in claim 6, wherein said inspection tool
is configured to display said second voltage contrast image with
signals corresponding to said metal silicide defects that are
pipes.
8. The method as recited in claim 6, wherein said second voltage
contrast image is subtracted from said voltage contrast image to
provide a voltage contrast difference image displaying signals
corresponding to metal silicide defects that are nubs.
9. The method as recited in claim 1, wherein said voltage contrast
image is one of a plurality of voltage contrast images for said
portion, each one of said plurality of voltage contrast images is
obtained using one of a set of collection fields ranging from less
positive to more positive than said impinging field; and said
inspection tool is configured to display said plurality of voltage
contrast images having signals corresponding to metal silicide
defects and to measure a change in intensity of said signals as a
function of a difference between said collection field and said
impinging field.
10. An inspection system for detecting metal silicide defects in a
microelectronic device, comprising: an inspection tool comprising
an electron-beam source and a collection optical unit; a stage
configured to position a portion of a semiconductor substrate in a
field of view of said inspection tool; and a control module
configured to: adjust an electron-beam landing energy applied by
said electron-beam source to said semiconductor substrate and
thereby produce an incident field on a surface of said
semiconductor substrate; adjust a detection potential applied to
said collection optical unit to thereby produce a collection field
that is stronger than said incident field; and produce a voltage
contrast image of said portion, and use said voltage contrast image
to determine a metal silicide defect in a microelectronic
device.
11. The inspection system as recited in claim 10, wherein said
collection field is at least about 8 percent stronger than said
incident field.
12. The inspection system as recited in claim 10, wherein said
control module is further configured to convert a first data set
from said collection optical unit into a voltage contrast image of
said portion, said voltage contrast image having signals
corresponding to metal silicide defects that are pipes or nubs.
13. The inspection system as recited in claim 12, wherein said
control module is further configured to: adjust said electron-beam
landing energy to thereby produce a second incident field on said
surface; adjust said detection potential to thereby produce a
second collection field that is weaker than said second incident
field; and convert a second data set from said collection optical
unit into a second voltage contrast image of said portion, said
second voltage contrast image having signals corresponding to metal
silicide defects that are pipes.
14. The inspection system as recited in claim 13, wherein said
control module is further configured to subtract said second data
set from said first data set to produce a third data set, and to
convert said third data set into a difference voltage contrast
image having signals corresponding to metal silicide defects that
are nubs.
15. The inspection system as recited in claim 13, wherein said
control module is further configured to direct said inspection tool
to sequentially collect said first and second data set from said
portion before commanding said stage to move a different portion of
said substrate in said field of view.
16. A method of manufacturing an integrated circuit comprising:
forming a microelectronic device on a semiconductor substrate;
forming metal silicide electrodes for said semiconductor device;
and inspecting said microelectronic device for metal silicide
defects by: positioning a portion of said semiconductor substrate
in a field of view of an inspection tool; producing a voltage
contrast image of said portion, wherein said voltage contrast image
is obtained using a collection field that is stronger than an
incident field; and using said voltage contrast image to determine
a presence of a metal silicide defect in said microelectronic
device.
17. The method as recited in claim 16, wherein said inspecting said
microelectronic device comprise steps in a front-end of line
process.
18. The method as recited in claim 17, wherein further
front-end-of-line processing of said microelectronic device is
halted if said metal silicide defect is detected.
19. The method as recited in claim 17, wherein one or more steps in
said front-end-of-line process are modified if said metal silicide
defect is detected.
20. The method as recited in claim 16, further comprising forming
interconnect metals lines on one of more insulating layer located
over said microelectronic device and coupling said interconnects
with said metal silicide electrodes to form an operative device if
said metal silicide defect is not severe.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is directed, in general, to a method
and system for detecting metal silicide defects in microelectronic
devices during the manufacture of integrated circuits.
BACKGROUND OF THE INVENTION
[0002] Metal silicides are commonly used as contact materials for
active areas of microelectronic devices, such as transistors having
source and drain regions and gate regions. Unfortunately, a number
of problems have been encountered when manufacturing devices having
metal silicide electrodes. In some cases, unacceptable numbers of
nonfunctional transistors are constructed because of the presence
of a gross short circuit caused by silicide defects. In other
instances, silicide defects from the source and drain regions punch
through the source/drain junction into the semiconductor substrate,
resulting in a large leakage current. In still other cases, there
is a large diode leakage between the source and drain regions and
the semiconductor substrate. These problems contribute to the
production of unacceptably low yields of transistors that operate
within performance specifications.
[0003] Traditional methods and instruments to detect metal silicide
defects have typically been performed on a completed
microelectronic device, that is, after completing all
front-end-of-line (FEOL) and back-end-of-line (BEOL) processes, as
part of quality assurance monitoring. Examples of conventional
detection methods include assessing the electrical or logic
performance characteristics of the device by measuring leakage
current or bit failure rates, or inspecting scanning electron
microscopic images of the device. The recent introduction of
electron-beam passive voltage contrast detection methodology and
instrumentation has greatly facilitated the measurement of
sub-surface metal silicide defects earlier in the manufacturing
process.
[0004] Importantly, improvements in voltage contrast imaging have
reduced the time to measure silicide shorts, thereby allowed such
imaging as part of FEOL processes. The metal silicide defects
detected by this approach, however, are limited to gross shorts
manifesting, for example, as metal silicide pipes in semiconductor
devices. There is a continuing need to improve on the detection of
metal silicide defects in the FEOL process in order to further
reduce resource expenditure on the fabrication of devices that are
destined to be defective.
[0005] Accordingly, what is needed in the art is a method and
system for detecting silicide defects and potential defects in a
microelectronic device during the manufacture of an integrated
circuit that does not suffer from the limitations associated with
conventional approaches to defect detection.
SUMMARY OF THE INVENTION
[0006] To address the above-discussed deficiencies of the prior
art, the present invention provides in one embodiment, a method of
detecting metal silicide defects in a microelectronic device. The
method comprises positioning a portion of a semiconductor substrate
in a field of view of an inspection tool. The method also comprises
producing a voltage contrast image of the portion, wherein the
voltage contrast image is obtained using a collection field that is
stronger than an incident field. The method also comprises using
the voltage contrast image to determine a metal silicide defect in
the microelectronic device.
[0007] Another aspect of the present invention is an inspection
system for detecting metal silicide defects in a microelectronic
device. The inspection system comprises an inspection tool
comprising an electron-beam source and a collection optical unit.
The inspection system further comprises a stage configured to
position a portion of a semiconductor substrate in a field of view
of the inspection tool. The inspection system also comprises a
controller. The controller is configured to adjust an electron-beam
landing energy applied by the electron-beam source to the
semiconductor substrate and thereby produce an incident field on a
surface of the semiconductor substrate. The controller is also
configured to adjust a detection potential applied to the
collection optical unit to thereby produce a collection field that
is stronger than the incident field. The controller is further
configured to produce a voltage contrast image of the portion of
the semiconductor substrate, and use the voltage contrast image to
determine a metal silicide defect in a microelectronic device.
[0008] Still another aspect of the present invention is a method of
manufacturing an integrated circuit. The method comprises forming a
microelectronic device on a semiconductor substrate and forming
metal silicide electrodes for the microelectronic device. The
microelectronic device is inspected for metal silicide defects
using the method described above.
[0009] The foregoing has outlined preferred and alternative
features of the present invention so that those skilled in the art
may better understand the detailed description of the invention
that follows. Additional features of the invention will be
described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiments as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a more complete understanding of the present invention,
reference is now made to the following detailed description taken
in conjunction with the accompanying FIGUREs. It is emphasized that
various features may not be drawn to scale. In fact, the dimensions
of various features may be arbitrarily increased or reduced for
clarity of discussion. In addition, it is emphasized that some
circuit components may not be illustrated for clarity of
discussion. Reference is now made to the following descriptions
taken in conjunction with the accompanying drawings, in which:
[0011] FIG. 1 illustrates by flow diagram, selected steps in an
exemplary method of detecting metal silicide defects in a
microelectronic device according to the principles of the present
invention;
[0012] FIG. 2 presents a block diagram of an exemplary inspection
system of the present invention for detecting metal silicide
defects in a microelectronic device; and
[0013] FIGS. 3-5 illustrate cross-sectional views of selected steps
in an exemplary method of manufacturing an integrated circuit
according to the principles of the present invention.
DETAILED DESCRIPTION
[0014] The present invention benefits from the realization that
previous approaches using passive voltage contrast imaging to
detect silicide defects are inadequate because they do not predict
additional silicide defects that can form after FEOL processing.
Metal silicide defects are formed due to the diffusion of metal
ions from metal silicide electrodes into channels in the lattice
structure of the semiconductor substrate, thereby introducing
structural defects in the semiconductor substrate. Defect formation
is enhanced by both FEOL and BEOL thermal processing because
increased temperatures promote metal ion diffusion.
[0015] As part of the present invention, it was recognized that
there could be silicide defects that are too small to form a short
after FEOL thermal processing and therefore go undetected using
conventional approaches. In some process flows, however, a
considerable number of these small silicide defects can go on to
develop into shorts after BEOL thermal processing.
[0016] The small silicide defects go undetected because existing
methods and tools for detecting defects require the existence of an
actual short circuit in the microelectronic device being inspected.
Conventional methods and tools rely on a large number of secondary
electrons being emitted from a grounded structure in the
microelectronic device as compared to an analogous neighboring
microelectronic device with an ungrounded or floating structure.
The presence of a grounded structure, however, implies that a short
is present in the microelectronic device to create the ground. If
there is no short, such as the case where there is small silicide
defect, then there is insufficient voltage contrast to detect the
defect using conventional methods and systems for voltage contrast
imaging.
[0017] The present invention overcomes this limitation by providing
a method and system to detect both metal silicide defects that form
actual shorts after FEOL processing, as well as metal silicide
defects that will only form shorts, or cause high leakage currents,
after BEOL processing. The ability to accurately predict potential
metal silicide defects advantageously allows accelerated learning
and correction of problematic manufacturing flow processes, thereby
reducing resource expenditure on the fabrication of devices that
are destined to be defective.
[0018] The present invention is particularly advantageous for
detecting nickel silicide electrode induced defects. It should be
understood, however, that the scope of the present invention
includes detecting such defects in any microelectronic device
caused by the formation of an electrode comprising any transition
metal silicide. For the purposes of the present invention, a
transition metal is defined as any element in Periods 4-6 and
Groups 3-12 of the Periodic Table of Elements (International Union
of Pure and Applied Chemist Convention for designating Groups and
Periods), as well as alloys thereof.
[0019] One embodiment of the present invention is a method of
detecting metal silicide defects in a microelectronic device. FIG.
1 illustrates, by flow diagram, selected steps in an exemplary
method 100 performed according to the principles of the present
invention. The method comprises, in step 110, positioning a portion
of a semiconductor substrate in a field of view of an inspection
tool.
[0020] The semiconductor substrate, such as a silicon wafer,
comprises a plurality of integrated circuit (IC) dies. Each of the
IC dies has metal silicide electrodes formed on components of
microelectronic devices in the IC. For example, the microelectronic
devices can comprise nMOS, pMOS transistors and CMOS devices,
having metal silicide electrodes formed on source and drain as well
as gate structures.
[0021] Those skilled in the art would be familiar the use of an
electron-beam source to raster an incident electron-beam over the
surface of the semiconductor substrate within a particular field of
view that is appropriate for the inspection tool being used. For
example an eS20.TM. inspection tool (KLA-Tencor Inc., San Jose,
Calif.) can have a field of view of about 2 by 2 microns. The
portion of the semiconductor substrate selected for voltage
contrast imaging is equal to or less than the field of view
selected for the inspection tool.
[0022] The method also comprises producing a voltage contrast
image, in step 120, under conditions where the image is obtained
using a collection field that is stronger than an incident field.
The term incident field as used herein refers to an electrical
field associated with a potential developed on the surface of the
semiconductor substrate as a result of the impinging rastering
incident electron-beam. The term collection field as used herein
refers to an electrical field associated with a potential created
in a space above the semiconductor substrate to attract and enhance
the detection of secondary electrons that are generated. Both the
collection field and incident fields have a positive charge. Thus,
in the context of the present invention, a collection field that is
stronger than the incident field means that the collection field is
more positive than the incident field. In certain preferred
embodiments, the collection field is at least about 8 percent
stronger than the incident field.
[0023] The collection field can be adjusted to be stronger than the
incident field, in step 125, by adjusting one or both of a landing
energy associated with the incident electron beam or a detection
potential associated with a collection optical unit of the
inspection tool. The quantity of secondary electrons produced at
the surface of the semiconductor substrate depends upon the landing
energy, that is, the amount of energy in the incident electron-beam
at the surface of the semiconductor surface. The amount of
secondary electrons detected can be increased by applying a
detection potential to a grid or mesh of the collection optical
unit. A positive potential applied to the grid or mesh attracts the
negatively charged secondary electrons into the collection optical
unit.
[0024] In certain advantageous embodiments of the method 100, the
detection potential used to generate the collection field is
greater than the electron-beam landing energy that generates the
incident field. The extent to which the detection potential is made
greater than the electron-beam landing energy depends upon the
composition of the semiconductor substrate and microelectronic
device. For example, in some embodiments directed to the detection
of nickel silicide defects, the detection potential is at least
about 20 electron-Volts greater than the electron-beam landing
energy. In other embodiments, where tungsten contacts are formed on
nickel silicide electrodes, the detection potential preferably
ranges from about 20 electron-Volts to about 400 electron-Volts
greater than the electron-beam landing energy voltage. In other
embodiments, where copper contacts are formed on nickel silicide
electrodes, the detection potential preferably ranges from about 20
electron-Volts to about 800 electron-Volts greater than the
electron-beam landing energy voltage.
[0025] The method 100 further comprises using, in step 130 the
voltage contrast image to determine a metal silicide defect. The
inspection tool is configured using conventional procedures to
contrast differences in signal intensities received from different
areas of the microelectronic device. The tool is typically adjusted
to display gray-scale voltage contrast images in which metal
contacts appear as an intense white signal while insulating
material surrounding the contact appears as a low intensity dark
signal. Of course, the tool could be configured to display the
signal from the metal contact as a dark spot in a reverse contrast
image, or as a particular color in a color image, where colors are
coded according to a predefined range of signal intensities. A
metal contact that is coupled to a microelectronic device with a
metal silicide defect has a higher signal intensity than adjacent
metal contacts that are coupled to microelectronic devices with no
metal silicide defect.
[0026] To determine a metal silicide defect in step 130, the
inspection tool is configured to display the voltage contrast image
obtained in step 120 to have a signal corresponding to the metal
silicide defects that are pipes or nubs. As noted above, typically
the voltage contrast image depicts an intense white signal for
metal contacts that are coupled to a microelectronic device having
metal silicide pipes or nub defects. The ability to detect both
metal silicide pipe or nub defects using the method of the present
invention is in contrast to conventional methods. Conventional
methods of defect detection are capable of displaying signals
corresponding to metal silicide defects that are pipes only.
[0027] The terms pipes and nubs as used herein refers to the size
of the metal silicide defect, and in particular, the length of the
long axis of the defect, at the time of defect detection. For the
purposes of the present invention, a pipe refers to a
cylindrical-shaped metal silicide defect whose long axis is of
sufficient length to create a short circuit between one component
of a microelectronic device and another component of the same, or a
different adjacent, microelectronic device. A nub refers to a
similarly shaped metal silicide defect, with the exception that its
long axis is not long enough to create a short circuit between one
component of a microelectronic device and another component of the
same, or a different adjacent microelectronic device.
[0028] As noted above, metal silicide defects are thought to form
due to the diffusion of metal atoms from metal silicide electrodes
into channels in the lattice structure of the semiconductor
substrate. The distance that metal atoms diffuse through the
channel defines the length of the long axis of the pipe or nub.
This diffusion distance depends on numerous factors, including the
chemical identity of the metal atom, the size of the channel, and
the duration and magnitude of temperature elevations that the
semiconductor substrate is subjected to.
[0029] Additionally, the characterization of a metal silicide
defect as a pipe or nub in step 130 depends upon the technology
node of interest. The design rules for a particular technology node
will govern the minimum separation distance between individual
microelectronic devices and the dimensions and separation between
components within a microelectronic device. The smaller the
technology node, the shorter the long axis of the pipe has to be to
cause a short circuit. One of ordinary skill in the art would
understand how to adjust the definition of pipes and nubs for the
technology node of interest.
[0030] Consider as a non-limiting example, a 65-nanometer
technology node, where the design rules specify a gate length of
about 65 nanometers and a source drain region length of about 1 to
3 times the gate length. In this situation, a metal silicide pipe
defect causing a short circuit between the source drain region and
the semiconductor substrate under the gate is estimated to have a
long axis of at least about 20 nanometers. In some applications of
the method 100, nubs having a long axis as small as about 5
nanometers can be detected.
[0031] It is emphasized that the characterization of a metal
silicide defect as a pipe or nub refers to the status of the defect
at the time the method 100 is performed. Preferably, the method 100
is performed as part of the FEOL process, and even more preferably,
after completing all thermal processes in the FEOL process. As
noted above, if the microelectronic device is subjected to
additional temperature increases during BEOL thermal processes,
then the metal atoms can diffuse an additional distance through
channels of the substrate, which in turn, can transform a nub into
a pipe. The voltage contrast image obtained in step 120 can detect
both pipes and nubs in the FEOL process, thereby providing an early
warning of metal silicide defects with the potential to cause the
microelectronic device to not operation within performance
specifications.
[0032] In some applications, a decision is made in step 135, to
differentiate between pipes and nubs appearing in the voltage
contrast image obtained in step 120. In this case, a second voltage
contrast image for the same portion of the semiconductor substrate
is obtained in step 140 under conditions where a second collection
field is weaker than a second incident field. In the context of the
present invention, a weaker field means that the second collection
field is less positive than the second incident field. Similar to
that discussed above, the collection field can be adjusted to be
weaker than the incident field, in step 145, by adjusting one or
both of the landing energy or a detection potential. In some cases,
it is desirable to set the second incident field to be
substantially equal to the incident field used to collect the first
voltage contrast image, and to adjust the second collection field
to be weaker than the incident field.
[0033] The inspection tool can be configured to display the second
voltage contrast image obtained in step 140 with signals
corresponding to metal silicide defects that are pipes. To
differentiate pipes and nubs, the second voltage contrast image
obtained in step 140 is subtracted from the voltage contrast image
obtained in step 120, to provide a voltage contrast difference
image in step 150. The inspection tool can then be configured to
display signals in the voltage contrast difference image
corresponding to metal silicide defects that are nubs.
[0034] In some cases it is advantageous to obtain, in step 160, a
plurality of voltage contrast images for the same portion of the
semiconductor substrate. In such instances, the first and second
voltage contrast images obtained in steps 120 and 140,
respectively, can each be one of the plurality of images.
Preferably, each one of the plurality of voltage contrast images is
obtained using one of a set of collection fields that range from
less positive to more positive than the impinging field. Of course,
the plurality of voltage contrast images can be obtained by
adjusting one or both of the impinging and collection fields. The
inspection tool can be configured to display the plurality of
voltage contrast images with signals corresponding to metal
silicide defects. Such a display of the plurality of images is
advantageous in situations such as a new fabrication process, where
it is uncertain what combination of impinging and collection fields
are appropriate to detect metal silicide defects that correspond to
pipes and nubs.
[0035] In some cases, the inspection tool is also configured, in
step 165, to measure a change in intensity of the signals as a
function a difference in the field strength (.DELTA. field) between
the collection field and the impinging field. In instances where
the impinging field is held constant and the collection field is
adjusted between scans, it is acceptable to measure the change in
intensity of the signals as a function of the changing collection
field. In still other instances, it is acceptable to measure the
change in intensity of the signals as a function of the changing
detection potentials used to generate the collection fields.
[0036] The change in intensity of the signal corresponding to the
metal silicide defects as function of the .DELTA. field is used to
predict a severity of the defect. In some cases, it is sufficient
for the severity to simply be a characterisation of the metal
silicide defect as a pipe or nub, similar to that obtained by
obtaining the difference image in step 150. In other cases,
however, the severity is a probability that after further
processing, the metal silicide defect corresponding to a nub will
form into a defect structure such as a pipe that causes a short
circuit or an unacceptable leakage current or other malfunctions in
the microelectronic device. As an example, a signal from a metal
silicide defect that has a large change in intensity per unit
.DELTA. field has a high probability of corresponding to defect
that is either already a pipe, or a nub that could easily become a
pipe upon further exposure to thermal processes.
[0037] If it is determined in step 170 that the entire
semiconductor substrate has been inspected, then the method 100 is
halted at step 180. Alternatively, if the entire semiconductor
substrate has not been inspected, then in step 190, a next portion
of the semiconductor substrate is positioned in the field of view
of the inspection tool, and steps 120 through 180 are repeated as
appropriate on the next portion.
[0038] Yet another aspect of the present invention is an inspection
system for detecting metal silicide defects in a microelectronic
device. FIG. 2 presents a block diagram of an exemplary inspection
system 200 of the present invention. The inspection system 200
comprises an inspection tool 205. The inspection tool 205 comprises
an electron-beam source 207 and a collection optical unit 210. The
inspection system 200 also comprises a stage 212 configured to
position a portion 215 of a semiconductor substrate 217 having a
surface 218 in a field of view 220 of the inspection tool 205. For
the embodiment shown in FIG. 2 the portion 215 of the substrate 217
selected for inspection is substantially the same size as the field
of view 220.
[0039] The inspection system 200 further comprises a control module
225. The control module 225 can comprise any conventional
processing device capable of performing operations needed to
control the inspection of microelectronic devices, and include
components well known to those skilled in the art. Such components
can include a bus 230 to send commands to and receive data from the
inspection tool 205, a program file 232 to control the inspection
tool 205, a memory 234 to hold data obtained by the inspection tool
205, processing circuitry 236 to perform mathematical operations on
the data.
[0040] The control module 225 is configured to adjust a landing
energy of an incident electron-beam 240 applied by the
electron-beam source 207 to the semiconductor substrate 217 and
thereby produce an incident field 242 on the substrate surface 218.
The control module 225 is also configured to adjust a detection
potential applied to the collection optical unit 210 to thereby
produce a collection field 245 that is stronger than the incident
field 242. The control module 225 is further configured to produce
a voltage contrast image 250 of the portion 215. As illustrated in
FIG. 2, the voltage contrast image 250 can be displayed on a video
monitor 255 that is coupled to the control module 225 via a data
cable 257.
[0041] The control module 225 is also configured to use the voltage
contrast image 250 to determine one or more metal silicide defects
260 in a microelectronic device 265. Any of the embodiments of the
methods and components discussed above and illustrated in FIG. 1,
can be used by the inspection system 200, to determine and
characterize the metal silicide defect. Consider the following
example of how the control module 225 can be configured to convert
a first data set from the collection optical unit 210 into a
voltage contrast image 250 of the portion 215 of the substrate
218.
[0042] The program file 232 of the control module 230 can configure
the inspection tool 205 to produce a collection field 245 that is
at least about 8 percent stronger than the incident field 242. A
first data set obtained from the inspection tool 205 using these
relative field strengths is stored in the memory 234 of the control
module 230. The processing circuitry 236 operates on the first data
set to convert it into the voltage contrast image 250 of the
portion 215. Because the collection field 245 is stronger than the
incident field 242, the voltage contrast image 250 has signals 270
corresponding to metal silicide defects 260 that are pipes or
nubs.
[0043] To further differentiate the metal silicide defects 260, the
control module 225 can be further configured to adjust the
electron-beam's 235 landing energy to produce a second incident
field on the substrate surface 245 and adjust the detection
potential to produce a second collection field that is weaker than
the second incident field. A second data set obtained from the
collection optical unit 210 under these conditions can then be
converted into a second voltage contrast image of the same portion
215 of substrate 217. The second voltage contrast image has signals
corresponding to metal silicide defects that are pipes only.
[0044] The control module 225 is further configured to subtract the
second data set from the first data set to produce a third data
set. The control module 225 is also configured to convert the third
data set into a difference voltage contrast image having signals
corresponding to metal silicide defects that are nubs. To minimize
the time to collect such data, it is advantageous for the control
module 225 to be configured to direct the inspection tool 205 to
sequentially collect the first and second data set from the same
portion 215 of the substrate 217 before commanding the stage 212 to
move a different portion of the substrate 217 into the field of
view 220. Of course, the control module 225 can be configured to
obtain a plurality of voltage contrast images of the same portion
217 of the substrate 218 in order to further characterize the
severity of metal silicide defects.
[0045] Still another aspect of the present invention is a method of
manufacturing an integrated circuit. FIGS. 3-5 illustrate
cross-sectional views of selected steps in an exemplary method of
manufacturing an integrated circuit 300 according to the principles
of the present invention. Turning first to FIG. 3, illustrated is
the partially completed integrated circuit 300 after forming a
microelectronic device 310 on a semiconductor substrate 315 and
forming metal silicide electrodes 320 for the microelectronic
device 310. Some preferred embodiments of the microelectronic
device 310 comprise an nMOS transistor 330 and a pMOS transistor
335 that form a microelectronic device 310 that is a CMOS device.
However, the microelectronic device can also comprise Junction
Field Effect transistors, bipolar transistors, biCMOS transistors,
or other conventional device components, and combinations
thereof.
[0046] Any conventional methods and materials can be used to
fabricate the microelectronic device 310 and metal silicide
electrodes 320. Typically forming the microelectronic device 310
and metal silicide electrodes 320 comprise steps in a FEOL process.
Included in the FEOL process are thermal processes to react a
transition metal layer deposited on structure of the
microelectronic device 310, such as source and drain structures
340, 345 and gate structures 350 to form the metal silicide
electrodes 320. These and other thermal processes can also result
in the formation of metal silicide defects, which are illustrated
in FIG. 3 as pipes 360 and nubs 365.
[0047] With continuing reference to FIG. 3, FIG. 4 illustrates the
integrated circuit 300 after forming contacts 400, 410, 420, such
as tungsten or copper contacts in an insulating layer 440, such as
a silicon dioxide layer, located over the semiconductor device 320.
One or mote of the contacts 400, 410, 420 are connected to the
metal silicide electrodes 320. FIG. 4 further illustrates
inspecting the microelectronic device 310 for metal silicide
defects 360, 365. Any of the above-described methods and systems
and their component parts, such as an inspection tool 450, can be
used to facilitate the inspection. For instance, the inspection can
comprise positioning a portion of the semiconductor substrate 315
in a field of view of the inspection tool 450, producing a voltage
contrast image using a collection field that is stronger than an
incident field and using the voltage contrast image to determine a
presence of a metal silicide defect 360, 365 in the microelectronic
device 310.
[0048] Preferably, the inspection comprise steps in a FEOL process,
because then the FEOL process can be halted if the metal silicide
defect 360, 365 is detected, thereby saving manufacturing resources
and time. Alternatively, one or more steps in the manufacturing
process can be modified if a metal silicide defect 360, 365 is
detected. One of ordinary skill in art would be aware of the
multitude of modifications that could be made to reduce or
eliminate the metal silicide defects. For example, the thermal
budget that the microelectronic device is exposed to during one or
both of FEOL and BEOL processes can be reduced. As another example,
a thinner transition metal layer can be deposited on one or more of
the source, drain and gate structures.
[0049] If no metal silicide defect is detected, or if the defect is
judged to be not severe, then the manufacture of the integrated
circuit 300 is completed. FIG. 5 illustrates the integrated circuit
after forming one or more interconnect metals lines 500, 510, 520
on one or more insulating layers 530, 540 to interconnect the
microelectronic device 310 and thereby to form an operative device.
Of course, the characterization of a defect as being not severe
based on the above-described inspection will be informed and
refined by the experiences gathered while manufacturing a plurality
of integrated circuits using the same or similar processes.
[0050] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without
departing from the scope of the invention in its broadest form.
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